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JP4477150B2 - Organic thin film EL device - Google Patents

Organic thin film EL device Download PDF

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Publication number
JP4477150B2
JP4477150B2 JP00549396A JP549396A JP4477150B2 JP 4477150 B2 JP4477150 B2 JP 4477150B2 JP 00549396 A JP00549396 A JP 00549396A JP 549396 A JP549396 A JP 549396A JP 4477150 B2 JP4477150 B2 JP 4477150B2
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organic
light emitting
emitting medium
thin film
medium
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JP00549396A
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JPH09199276A (en
Inventor
功二 宇津木
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Samsung Display Co Ltd
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Samsung Mobile Display Co Ltd
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    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10KORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00Organic light-emitting devices
    • H10K50/10OLEDs or polymer light-emitting diodes [PLED]
    • H10K50/11OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/125OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers specially adapted for multicolour light emission, e.g. for emitting white light
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00Electroluminescent light sources
    • H05B33/12Light sources with substantially two-dimensional radiating surfaces
    • HELECTRICITY
    • H10SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10KORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/30Devices specially adapted for multicolour light emission
    • H10K59/32Stacked devices having two or more layers, each emitting at different wavelengths
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00Stock material or miscellaneous articles
    • Y10S428/917Electroluminescent

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  • Optics & Photonics (AREA)
  • Electroluminescent Light Sources (AREA)

Description

【0001】
【発明の属する技術分野】
本発明は白色発光やフルカラー表示等に利用できる有機薄膜EL素子に関する。
【0002】
【従来の技術】
タング(Tang)とバンスリィク(VanSlyke)らの新しい構成の有機薄膜EL素子の報告(アプライド・フィジックス・レターズ(AppliedPhysics Letters)、51巻、913頁、1987年)以来、有機材料と素子化技術の改良により、種々の発光色を比較的容易に得ることが可能になった。特に、青、緑、赤の3原色発光が得られるようになったことから、フルカラー素子の開発も進められている。
【0003】
有機薄膜EL素子を使ったフルカラ−化の方法の一つとして、青(B)、赤(R)、緑(G)の発光材料を積層薄膜化する方法が報告されている(第253回蛍光体同学会講演予稿、1頁〜8頁、1994年、特開平7−142169号公報参照)。前記方法は図4に示すように基板上に、有機青色発光媒体、有機緑色発光媒体、有機赤色発光媒体が形成され、一対の電極から電子と正孔を注入し発光媒体中で電子と正孔が再結合することによって生じる発光を基板側から取り出している。この場合、各発光媒体から生じる発光を合成、すなわち発光スペクトルを重ね合わせることで白色発光を実現している。この方法においては、基本的に有機薄膜層を2次元(平面)方向に素子分離することなく、R,G,Bのパターンニングはカラーフィルターを用いて行えるので、有機薄膜はベタの成膜で良いことがこの方法の利点の一つである。
【0004】
発光スペクトルを重ね合わせて光を取り出す別な方法として、有機EL素子(セル)を2枚以上重ね合わせ、各単位セルにおいて発生した光を合成して取り出方法が開示されている(特開平7−57873号公報参照)。この方法を用いると、高解像度の合成発光が実現できると述べられている。
【0005】
【発明が解決しようとする課題】
前述したように、発光層が積層された有機薄膜EL素子と複数の有機ELセルが重なって形成される有機薄膜EL素子においては、比較的簡単な構造と手法で白色発光やカラー化が実現できる。しかし、前記2つの方法では、いずれも発光色の色バランスの制御が困難であること、発光の駆動電圧が高くなること、発光効率(光子/電子変換効率、光取り出し効率)が低いなどの問題がある。
【0006】
例えば、白色発光を得ようとする場合、図4の従来の素子では輝度バランスを制御するには、発光材料の含有量を精密に制御する必要があること、電圧によって輝度バランスが変動すること、及び同一発光層中に複数の発光材料が存在するため電荷トラップが生じやすく低電圧駆動ができない等の欠点を有する。また、図5のようなセルを複数個重ね合わせる方法で白色発光やカラー表示を行う場合、セル間の電極の短絡を防ぐための絶縁膜層が必要なこと、且つセルが複数個重なっているために電極や絶縁膜等による光の透過率が低くなり、結果として高輝度発光がきわめて困難である。
【0007】
本発明の目的は、有機発光媒体が適切に積層された高発光効率の有機薄膜EL素子で、特に高輝度の白色発光やフルカラー発光を簡単な手法で得るための素子構成を提供することにある。
【0008】
【課題を解決するための手段】
本発明者は全述の課題を解決するために、発光の輝度バランスを制御することが容易で、しかも発光輝度の高い合成発光及びカラー発光を得るべく検討した結果、複数の積層された有機発光媒体の界面に電極を設け、前記電極からは隣接する有機発光媒体の両方に電荷が注入できるようにすることで、同一基板状上で比較的容易に合成発光が得られることを見いだし本発明に至った。
【0009】
すなわち本発明は、基板上に少なくとも一方が透明な複数の電極によって挟持された複数の積層された有機発光媒体を有する有機薄膜EL素子において、前記複数の積層された有機発光媒体は本質的に青色発光、緑色発光、赤色発光をする各層をこの順に積層してなり、前記複数の積層された有機発光媒体の少なくとも赤色発光をする層と緑色発光をする層との界面に隣接する二つの有機発光媒体の両方に電荷を注入できる電極を有し、前記複数の電極と有機発光媒体の界面に設けられた電極が、負極と正極が交互となるように設定され、前記複数の電極のうち赤色発光をする層に接する側の電極が、他方の電極よりも仕事関数が小さな材料よりなることを特徴とする有機薄膜EL素子である。ここで、複数の電極と有機発光媒体の界面に設けられた電極が、負極と正極が交互となるように設定するとは、例えば基板上の電極が正極のとき、基板上の電極に最も近い界面に設けられた電極は負極、次に積層される電極は正極となるように電極を設けることである。また、有機発光媒体が、本質的に青色発光、緑色発光、赤色発光をする各層を設け、3つの発光媒体を複数個同時に発光させることで基板から白色等の合成色発光を取り出し、カラーフィルターと組み合わせてフルカラー表示を行うことも可能である。なお、以下前記「複数の電極」は、便宜上「対電極」と述べるが、これは正極と負極の組み合わせを言うのではなく、複数の積層された有機発光媒体を挟持するために対を成していることを指す。

【0010】
また、本発明の有機薄膜EL素子の発光媒体を構成する有機発光層は正孔注入・輸送帯及び/又は電子注入・輸送帯との積層構造であったり、発光材料単体又は発光材料と正孔輸送材料及び/又は電子輸送材料の混合体から形成される多層又は単層構造であってもよい。
【0011】
図1に示す例では、積層された複数の有機発光媒体のうち、有機赤色発光媒体3cと有機緑色発光媒体3bとの間に半透明陽極4aが設けられている。図1において電極4aからは隣接する有機発光媒体の両方、すなわち図1では有機緑色発光媒体3bと有機赤色発光媒体3cに素子が構成されている。また、半透明陰極2aと陰極2cは共通に電源に接続されている。半透明陰極2aからは有機青色発光媒体3a及び有機緑色発光媒体3bに、また陰極2cからは有機赤色発光媒体3cに電子が注入され、電極4aから注入された正孔と再結合して各有機発光媒体がELを発光する。各有機発光媒体からかのELは合成され基板を通して取り出すことができる。
【0012】
図1において陰極2cの仕事関数を半透明陰極2aの陰極よりも小さくしておけば有機赤色発光媒体3cの電子注入効率を他の有機発光媒体への注入よりも上げることが可能であり、例えば赤色発光の発光効率が低い材料系を用いても、緑色発光媒体3bと青色発光媒体3aとの輝度バランスの制御が従来の方法よりも簡単になる。また、図1においては光を取り出す光路中に存在する電極が2個で済み、更に発光セルを複数個重ねる従来の方法(図5)のように絶縁膜又は基板を設ける必要はないので光の取り出し効率の低減を少なくできる利点がある。
【0013】
図1では、3つの有機発光媒体の内2つが同じ電極対の間に形成されているが、本発明においては図3に示すように、有機発光媒体を分割する電極を二つ設け、有機赤色発光媒体3c、有機緑色発光媒体3b及び青色発光媒体3aを独立させれば発光の輝度バランスの制御がより簡単になる。尚、図1においては電源が1つで半透明陰極2aと陰極2cが、図3においては半透明陰極2bと陰極2c及び半透明陽極4bと半透明陽極4aが共通に接続されているが、電源を複数個にして各発光媒体に電圧を独立に印加して、輝度バランスを制御してもよい。
【0014】
本発明において、有機薄膜EL素子における有機発光媒体の有機薄膜層は真空蒸着法、分子線蒸着法(MBE法)あるいは溶媒に溶かした溶液のディッピング法、スピンコーティング法、キャスティング法、バーコート法、ロールコート法等の塗布法による公知の方法で形成することができる。有機発光媒体の発光材料は特に限定されず、公知の発光材料を適用できる。有機青色発光媒体を構成する青色発光材料としては、例えば、米国特許第541671号や米国特許第5294870号に記載される8−キノリノール及びその誘導体の金属錯体や前記金属錯体にペリレンやクマリン誘導体をドープしたもの、特開平6−9953号公報に示されるジスチリルアリーレン誘導体及びジスチリルアリーレン誘導体に蛍光色素をドープしたものなどが性能が優れており代表として挙げられる。有機緑色発光媒体を形成する発光材料としては、例えば、トリス(8−キノリノラト)アルミニウム、キナクリドン誘導体、キサンテン色素、クマリン誘導体、などが性能が優れており代表として挙げられる。有機赤色発光媒体を形成する発光材料としてはアジン色素、クマリン誘導体、キサンテン色素、メロシアニン色素、アクリジン色素、フタロシアニン色素等が挙げられる。
【0015】
本発明有機薄膜EL素子の有機発光媒体には、必要に応じて正孔注入・輸送層を設けることも有効である。正孔輸送材料としては特に限定されないが、例えばトリフェニルジアミン誘導体、オキサジアゾール誘導体、ポルフィリン誘導体、スチルベン誘導体、アリールアミン誘導体などを用いることができる。本発明では、発光効率を上げるため、前記正孔輸送層と発光層の間にブロッキング層を設けることも有効である。前記ブロッキング層は、発光層内で生成した励起子の閉じ込めと陰極から発光層に注入された電子の閉じ込めを担っている。前記ブロッキング層に用いるべく化合物としては、極度に正孔の注入特性を阻害するものでなければ特に限定されるものではないが、励起エネルギ−が隣接する発光層材料のそれよりも大きいことが望ましい。本発明においてブロッキング層として適用できる化合物としては、発光効率を低減させない範囲で、例えば公知のトリフェニルジアミン誘導体、オキサジアゾール誘導体、ヒドラゾン誘導体、ブタジエン誘導体、スチリル誘導体、ピラゾリン誘導体、ベンジジン誘導体などが挙げられる。更に、本発明においては正孔輸送層と陽極の間に正孔注入層を設けることも有効である。正孔注入層は陽極からの安定な正孔注入を達成すべく導入するものであるが、有機薄膜層と陽極の密着性を保持する役目を担う必要がある(応用物理、第64巻、第12号、1230頁〜1233頁参照)。本発明において適用できる正孔注入層は例えば“色素ハンドブック:講談社’86年”に記載されているスピロ化合物、アゾ化合物、キノン化合物、インジゴ化合物、ジフェニルメタン化合物、キナクリドン化合物、ポリメチン化合物、アクリジン化合物、ポルフィリン化合物等の縮合多環系の色素が適用できる。また、芳香族アミン等の“オーガニック セミコンダクターズ:フェルラック ケミエ社’74年(ORGANIC SEMICONDUCTORS:VERLAG CHEMIE’74)”に記載されている低分子有機P型半導体も適用できる。
【0016】
本発明においては必要に応じて電子注入・輸送帯を発光層と陰極の間に設けても良い。電子注入・輸送材料は特に限定されるものではないが、8−ヒドロキシキノリノール及びその誘導体、オキサジアゾール誘導体、ジフェニルキノン誘導体、SrO、CaO、BaOなどのアルカリ土類酸化物(特開平6−163158号公報参照)の適用が可能である。
【0017】
有機薄膜EL素子の陽極は、正孔を正孔輸送帯に注入する役割を担うものであり、4.0eV以上の仕事関数を有することが効果的である。陽極または半透明陽極材料の具体例としては、酸化インジウム錫合金(ITO)、酸化錫(SnO2 )、金、銀、白金、銅等を含んだ化合物が適用できる。陰極としては、電子輸送帯又は発光層に電子を注入する目的で、仕事関数の小さい材料が好ましく、特に限定されないが、具体的にはインジウム、アルミニウム、マグネシウム、マグネシウム−インジウム合金、マグネシウム−アルミニウム合金、アルミニウム−リチウム合金、アルミニウム−スカンジウム−リチウム合金等が使用できる。半透明な陰極材料としては特開平6−163158号公報に記載されるITOやSnO2 を用い、前記半透明な陰極材料と有機薄膜層の界面にSrO、CaOなどのアルカリ土類金属酸化物を0.1〜1nm設ければ効果的な電子注入が達成される。
【0018】
尚、素子を酸素や湿気から守る目的で、金属酸化物、金属硫化物、金属沸化物等の無機化合物や公知の有機化合物から構成される封止層を設ければ大気中でも長寿命の駆動が保証できる。
【0019】
【発明の実施の形態】
【実施例】
以下、本発明の実施例について詳細に説明するが、白色発光を得るための具体例を示し、比較例と比較している。
【0020】
(実施例1)
図1を参照しながら本発明の実施例1について説明する。以下に本発明の実施例1に用いる有機薄膜EL素子の作成手順について説明する。十分洗浄したガラス基板1上に半透明陰極であるSnO2 を形成した後、電子注入層であるSrOを0.5nm形成した。続いてMBE法にて超高真空下、電子輸送層のトリス(8−キノリノラト)アルミニウム(以下Alqと略記)を18nm形成した後、下記の化学式1に示されるジスチリルビフェニル誘導体(以下DPVBiと略記)を青色発光のホスト材料として用い、化学式2に示されるゲスト材料(以下BczVBiと略記)が前記ホスト材料に対して3.1モル%含まれるように超高真空下で35nm成膜し、有機青色発光媒体3aが完成する。
【0021】
【化1】

Figure 0004477150
【0022】
【化2】
Figure 0004477150
【0023】
次に、有機青色発光媒体3a上にAlqを超高真空下35nm形成し、更にAlq上に正孔輸送層としてN,N’−ビフェニル−N,N’−ビス(α−ナフチル)−1,1’−ビフェニル−4,4’−ジアミン(以下α−NPDと略記)を高真空下にて30nm形成し、有機緑色発光媒体3bが有機青色発光媒体3aと接する形で形成される。
【0024】
次に、インジウムと亜鉛からなる半透明陽極4aを低温プロセスにおいて200nm形成した後、有機赤色発光媒体3cの正孔輸送層であるα−NPDを高真空下で40nm形成し、更にAlqをホスト材料として用い、赤色蛍光色素である4−(ジシアノメチレン)−2−メチル−6−(p−ジメチルアミノスチリル)−4H−ピラン(以下DCMと略記)をゲスト材料として用い、DCMがAlqに対して1.8モル%含まれるように高真空下で50nm形成し、有機赤色発光媒体3cが形成される。
【0025】
最後に、陰極2cとしてスカンジウムが1モル%含まれるアルミニウム合金をアルゴンガス中でRFスパッタ法で蒸発し、リチウムを抵抗加熱源から蒸発させる方法でリチウムが陰極の0.3モル%を占めるように20nm形成した。更に、陰極の保護層としてスカンジウムが1モル%含まれるアルミニウム合金をアルゴンガス中のRFスパッタ法により300nm形成した。
【0026】
このようにして、R,G,Bの有機発光媒体を有する本発明の実施例1の有機薄膜EL素子が完成する。以上のようにして作成した有機薄膜EL素子に半透明陰極2aと陰極2cを共通に、また半透明陽極4aは単独で直流電源に接続して電圧を印加して発光させたところ、10Vで約4520cd/m 2 の輝度が得られた。図4に示す従来の構造を用いた比較例1と比較すると輝度が約3.6倍向上している。これは、本発明の有機薄膜EL素子を用いれば、比較例1に示す従来の素子よりもキャリヤー注入・輸送効率の向上や発光量子効率が向上したためと考えられる。また、100cd/m 2 におけるCIE色度座標はX=0.345,Y=0.361であり、白色の発光を取り出すことができた。
【0027】
(実施例2)
有機発光媒体のうち、有機青色発光媒体3aの電子輸送層であるAlqを18nm形成し、且つAlq上部に正孔輸送性のポリビニルカルバゾール(以下PVKと略記)バインダー中にDPVBiとBczVBiとがモル比で100:3になるように分散し、スピンコート法にて有機発光層を35nm形成しする以外は、実施例1と同様に有機薄膜EL素子を作成した。以上のようにして作成した有機薄膜EL素子に半透明陰極2aと陰極2cを共通に、また半透明陽極4aは単独で直流電源に接続して電圧を印加し発光させたところ、10Vで約2860cd/m 2 の輝度が得られた。比較例2と比較すると輝度が約2.9倍向上している。また、100cd/m 2 におけるCIE色度座標はX=0.328,Y=0.381でありほぼ白色の発光を取り出すことができた。
【0032】
実施例3)図3を参照しながら本発明の実施例3について説明する。実施例3は有機発光媒体が半透明電極により3分割されているところが実施例1から参考例2とは異なる。以下に本発明の実施例3に用いる有機薄膜EL素子の作成手順について説明する。十分洗浄したガラス基板1上に半透明陽極4bであるITOを形成した後、正孔注入層としてCuPcを5nm形成し、更にその上に正孔輸送層であるα−NPDを高真空下で40nm形成した。次に青色発光のホスト材料としてDPVBiを用い、ゲスト材料(BczVBi)が前記ホスト材料に対して3.1モル%含まれるように超高真空下で45nm形成した後、電子輸送層としてAlqを超高真空下20nm形成し、有機青色発光媒体3aが完成する。この有機青色発光媒体3aの上に有機青色発光媒体3aに電子を注入するための半透明陰極2bとして、SrOを0.5nm形成した後、更にインジウムと亜鉛からなる透明電極を積層し、更にその上部にSrOを0.5nm形成し、有機青色発光媒体3aと有機緑色発光媒体3bの両方に電子注入可能な半透明陰極2bが完成する。次に半透明陰極2b上に発光層であるAlqを50nm、正孔輸送層であるα−NPDを50nm形成し、有機緑色発光媒体3bが完成する。この有機緑色発光媒体3b上にインジウムと亜鉛からなる半透明陽極4aを形成した。続いて正孔輸送層のα−NPDを高真空下にて30nm形成し、Alqをホスト材料として用い、赤色蛍光色素であるDCMをゲスト材料として用い、DCMがAlqに対して1.8モル%含まれるように高真空下で50nm形成し、有機赤色発光媒体3cが形成される。最後に陰極2cとしてスカンジウムが1モル%含まれるアルミニウム合金をアルゴンガス中でRFスパッタ法で蒸発し、リチウムを抵抗加熱源から蒸発させる方法でリチウムが陰極の0.3モル%を占めるように20nm形成した。更に、陰極の保護層としてスカンジウムが1モル%含まれるアルミニウム合金をアルゴンガス中のRFスパッタ法により300nm形成した。
【0033】
このようにして、R,G,Bの有機発光媒体を有する本発明の実施例3の有機薄膜EL素子が完成する。以上のようにして作成した有機薄膜EL素子に半透明陰極2bと陰極2cを共通に、また半透明陽極4aと4b共通にして直流電源に接続して電圧を印加し発光させたところ、10Vで約4015cd/m 2 の輝度が得られた。図5に示す従来の発光セルを重ねた場合の構造を用いた比較例3と比較すると輝度が約4.7倍向上している。また、100cd/m2 におけるCIE色度座標はX=0.345,Y=0.371であり白色の発光を取り出すことができた。
【0034】
尚、本実施例では白色発光を得ているが、半透明電極によって分割されたR,G,Bの発光媒体の内、少なくとも1つを発光させないように駆動すれば白色以外の発光を得ることも可能である。
【0035】
実施例4)有機発光媒体のうち、有機青色発光媒体3aとしてPVKバインダー中にDPVBiとBczVBiとがモル比で100:3になるように分散し、スピンコート法にて有機発光層を70nm形成し、その上部に電子輸送層であるAlqを20nm形成する以外は、実施例3と同様に有機薄膜EL素子を作成した。以上のようにして作成した有機薄膜EL素子に半透明陰極2bと陰極2cを共通に、また半透明陽極4aと4b共通にして直流電源に接続して電圧を印加して発光させたところ、10Vで約3140cd/m2 の輝度が得られた。図5に示す従来の構造を用いた比較例4と比較すると輝度が約6倍向上している。これは、本発明の有機薄膜EL素子を用いることで、比較例4に示す従来の素子よりも光の取り出し効率が向上したためである。また、100cd/m2におけるCIE色度座標はX=0.344,Y=0.369であり白色発光を取り出すことができた。
【0036】
(比較例1)
以下に図4を参照しながら比較例1の有機薄膜EL素子について説明する。十分洗浄したガラス基板1上に半透明陽極4aであるSnO2 を形成した後順に、正孔輸送層であるα−NPDを超高真空下35nm形成し、次に有機青色発光媒体3aとしてDPVBiを青色発光のホスト材料として用い、ゲスト材料(BczVBi)が前記ホスト材料に対して3.1モル%含まれるように超高真空下35nm形成した。次に有機青色発光媒体3a上に有機緑色発光媒体3bとしてAlqを超高真空下35nm形成し、更にAlq上にAlqをホスト材料として用い、赤色蛍光色素であるDCMをゲスト材料として用い、DCMがAlqに対して1.8モル%含まれるように高真空下で30nm形成し、有機赤色発光媒体3cを形成した。最後に、陰極2cとしてスカンジウムが1モル%含まれるアルミニウム合金をアルゴンガス中でRFスパッタ法で蒸発し、リチウムを抵抗加熱源から蒸発させる方法でリチウムが陰極の0.3モル%を占めるように20nm形成した。更に、陰極の保護層としてスカンジウムが1モル%含まれるアルミニウム合金をアルゴンガス中のRFスパッタ法により300nm形成した。
【0037】
このようにして、R,G,Bの有機発光媒体が積層された本発明の比較例1の有機薄膜EL素子が完成する。以上のようにして作成した有機薄膜EL素子に直流電圧を印加し発光させたところ、10Vで約1270cd/m 2 の輝度が得られた。また、100cd/m 2 におけるCIE色度座標はX=0.267,Y=0.458であり、白色発光は得られなかった。
【0038】
(比較例2)
以下に比較例2の有機薄膜EL素子について説明する。十分洗浄したガラス基板1上に半透明陽極4aであるSnO2 を形成した後、順に正孔注入層であるCuPcを25nm形成し、更に有機青色発光媒体3aとして、PVKバインダー中にDPVBiとBczVBiとがモル比で100:3になるように分散し、スピンコート法にて有機発光層を70nm形成しする以外は、比較例1と同様に有機薄膜EL素子を作成し、評価を行った。比較例2で作成した有機薄膜EL素子に直流電圧を印加し発光させたところ、10Vで約970cd/m 2 の輝度が得られた。また、100cd/m 2 におけるCIE色度座標はX=0.277,Y=0.450であり、白色発光は得られなかった。
【0039】
(比較例3)
比較例3においては、図5に示すように有機発光セルを複数個積層して合成発光を得るための有機薄膜EL素子を作成した。以下に比較例3の有機薄膜EL素子の作成方法について説明する。十分洗浄したガラス基板1上に半透明陽極4bであるITOを形成した後、正孔注入層として銅フタロシアニン(以下CuPcと略記)を5nm形成し、更にその上に正孔輸送層であるα−NPDを高真空下で40nm形成した。次に青色発光のホスト材料としてDPVBiを用い、ゲスト材料(BczVBi)が前記ホスト材料に対して3.1モル%含まれるように超高真空下で45nm形成した後、電子輸送層としてAlqを超高真空下20nm形成した。その上に半透明陰極2bとして、SrOを0.5nm形成した後、インジウムと亜鉛からなる透明電極を低温プロセスにて積層し青色発光を示す第1の有機発光セルがする。この第1の発光セルの上に第1の発光セルと第2の発光セルを分離するためにGeOからなる絶縁膜5を25nm設けた。次に、前記GeO上に第2の有機発光セルにを形成する。GeO上にインジウムと亜鉛からなる半透明陽極4aを形成後、正孔輸送層であるα−NPDを50nm、発光層であるAlqを50nm形成する。次に、半透明陰極2bとして、SrOを0.5nm形成した後、インジウムと亜鉛からなる透明電極を積層し緑色発光を示す第2の有機発光セルがする。この第2の発光セルの上に第2の発光セルと第3の発光セルを分離するためにGeOからなる絶縁膜5を25nm設けた。次に、前記GeO上に第3の有機発光セルにを形成する。GeO上にインジウムと亜鉛からなる半透明陽極4aを形成後、正孔輸送層であるα−NPDを50nm形成し、発光層としてDCMがAlqに対して1.8モル%含まれるようにAlqを高真空下で50nm形成する。最後に陰極2cとしてスカンジウムが1モル%含まれるアルミニウム合金をアルゴンガス中でRFスパッタ法で蒸発し、リチウムを抵抗加熱源から蒸発させる方法でリチウムが陰極の0.3モル%を占めるように20nm形成した。更に、陰極の保護層としてスカンジウムが1モル%含まれるアルミニウム合金をアルゴンガス中のRFスパッタ法により300nm形成し、第3の有機発光セルが完成する。
【0040】
このようにして、有機発光セルが積層された本発明の比較例3の有機薄膜EL素子が完成する。以上のようにして作成した有機薄膜EL素子のそれぞれの有機発光セルを直流電源に接続して電圧を印加したところ、各発光セルに10V印加したところ約850cd/m 2 の発光が得られた。100cd/m 2 におけるCIE色度座標はX=0.286,Y=0.495であり、白色発光は得られなかった。
【0041】
(比較例4)
比較例4の有機薄膜EL素子の作成方法について説明する。十分洗浄したガラス基板1上に半透明陽極4bであるITOを形成した後、正孔注入層としてCuPcを25nm形成し、PVKバインダー中にDPVBiとBczVBiとがモル比で100:3になるように分散し、スピンコート法にて有機発光層を70nm形成し、その上部に電子輸送層であるAlqを20nm形成する以外は比較例3と同様にして有機発光セルが複数個重なってなる有機薄膜EL素子を作成した。
【0042】
以上のようにして作成した有機薄膜EL素子のそれぞれの有機発光セルを直流電源に接続して電圧を印加したところ、各は発光セルに10V印加したところ約525cd/m 2 の発光が得られた。100cd/m 2 におけるCIE色度座標はX=0.283,Y=0.461であり白色発光は得られなかった。
【0043】
【発明の効果】
複数の有機発光媒体が積層されてなる有機薄膜EL素子において、有機発光媒体の界面に電極を設け、前記電極からは隣接する有機発光媒体の両方に電荷を注入するようにし、各発光媒体の発光強度を電圧で制御することで、従来の有機発光媒体が積層されてなる有機薄膜EL素子において困難であった輝度バランスの制御が容易で且つ低電圧・高輝度の合成発光が得られる。また、従来の発光セルを複数個重ねて合成発光を取り出す方法よりも、光の取り出し効率が改善され、且つ製造プロセスが簡略化できる。
【図面の簡単な説明】
【図1】本発明の実施例1及び実施例2で用いた複数の発光媒体が積層されてなる有機薄膜EL素子の説明図である。
【図3】本発明の実施例3及び実施例4で用いた複数の発光媒体が積層されてなる有機薄膜EL素子の説明図である。
【図4】比較例1及び比較例2で用いた複数の発光媒体が積層されてなる従来の有機薄膜EL素子の説明図である。
【図5】比較例3で用いた有機ELセルを複数個重ねて発光を取り出す従来の有機薄膜EL素子の説明図である。
【符号の説明】
1 基板
2a 半透明陰極
2b 半透明陰極
2c 陰極
3a 有機青色発光媒体
3b 有機緑色発光媒体
3c 有機赤色発光媒体
4a 半透明陽極
4b 半透明陽極
5 絶縁膜
6a 有機青色発光セル
6b 有機緑色発光セル
6c 有機赤色発光セル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic thin film EL element that can be used for white light emission, full color display, and the like.
[0002]
[Prior art]
Improvements in organic materials and device technology since Tang and VanSlyke et al. Reported new organic thin-film EL devices (Applied Physics Letters, 51, 913, 1987) Thus, various emission colors can be obtained relatively easily. In particular, the development of full-color elements has been promoted since the emission of three primary colors of blue, green, and red can be obtained.
[0003]
As one of full color methods using an organic thin film EL element, a method of stacking thin films of blue (B), red (R), and green (G) light emitting materials has been reported (the 253rd fluorescence). Proceedings of the Dokdo Association, pages 1-8, 1994, see JP-A-7-142169). In the method, an organic blue light emitting medium, an organic green light emitting medium, and an organic red light emitting medium are formed on a substrate as shown in FIG. 4, and electrons and holes are injected from a pair of electrodes. The light emitted from the recombination is extracted from the substrate side. In this case, white light emission is realized by synthesizing the light emitted from the light emitting media, that is, by superimposing the light emission spectra. In this method, R, G, B patterning can be performed using a color filter without basically separating the organic thin film layer in a two-dimensional (planar) direction. Good is one of the advantages of this method.
[0004]
As another method for extracting light by superimposing emission spectra, a method is disclosed in which two or more organic EL elements (cells) are overlapped and light generated in each unit cell is synthesized (Japanese Patent Laid-Open No. 7). -57873). It is stated that high-resolution combined light emission can be realized by using this method.
[0005]
[Problems to be solved by the invention]
As described above, in an organic thin film EL element in which an organic thin film EL element in which a light emitting layer is laminated and a plurality of organic EL cells are overlapped, white light emission and colorization can be realized with a relatively simple structure and method. . However, in both of the above two methods, there are problems such as difficulty in controlling the color balance of the light emission color, an increase in the light emission drive voltage, and low light emission efficiency (photon / electron conversion efficiency, light extraction efficiency). There is.
[0006]
For example, when trying to obtain white light emission, in order to control the luminance balance in the conventional element of FIG. 4, it is necessary to precisely control the content of the luminescent material, the luminance balance varies depending on the voltage, In addition, since a plurality of light emitting materials are present in the same light emitting layer, charge traps are likely to occur and low voltage driving cannot be performed. In addition, when white light emission or color display is performed by overlapping a plurality of cells as shown in FIG. 5, an insulating film layer for preventing a short circuit of electrodes between the cells is necessary, and a plurality of cells are overlapped. For this reason, the light transmittance due to the electrode, the insulating film or the like is lowered, and as a result, high-luminance emission is extremely difficult.
[0007]
An object of the present invention is to provide an organic thin film EL element having a high luminous efficiency in which organic light emitting media are appropriately laminated, and particularly to provide an element configuration for obtaining high luminance white light emission or full color light emission by a simple method. .
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, the present inventor has studied to obtain a composite light emission and a color light emission that are easy to control the luminance balance of light emission and have a high light emission luminance. It has been found that synthetic light emission can be obtained relatively easily on the same substrate by providing an electrode at the interface of the medium and allowing charge to be injected into both of the adjacent organic light emitting media from the electrode. It came.
[0009]
That is, at least one of the present invention is transparent on the substrate.Multiple electrodesIn an organic thin film EL element having a plurality of stacked organic light emitting media sandwiched byThe plurality of stacked organic light emitting media are formed by sequentially stacking layers emitting blue light, green light, and red light in this order, and at least red light emitting layers and green layers of the plurality of stacked organic light emitting media. An electrode capable of injecting charges into both of the two organic light-emitting media adjacent to the interface with the light-emitting layer, and the electrodes provided at the interface between the plurality of electrodes and the organic light-emitting medium are alternately negative and positive electrodes The organic thin film EL element is characterized in that the electrode on the side in contact with the layer emitting red light among the plurality of electrodes is made of a material having a work function smaller than that of the other electrode. Here, the electrode provided at the interface between the plurality of electrodes and the organic light emitting medium is set so that the negative electrode and the positive electrode are alternated. For example, when the electrode on the substrate is a positive electrode, the interface closest to the electrode on the substrate The electrode provided in is to be a negative electrode, and the electrode to be laminated next is to be a positive electrode. In addition, the organic light emitting medium is provided with layers that emit blue light, green light, and red light, and a plurality of three light emitting media emit light at the same time. It is also possible to perform full color display in combination. Hereinafter, the “plural electrodes” will be referred to as a “counter electrode” for the sake of convenience, but this does not mean a combination of a positive electrode and a negative electrode, but forms a pair to sandwich a plurality of stacked organic light emitting media. It points to that.

[0010]
Further, the organic light emitting layer constituting the light emitting medium of the organic thin film EL device of the present invention has a laminated structure of a hole injection / transport zone and / or an electron injection / transport zone, a light emitting material alone or a light emitting material and a hole. It may be a multilayer or a single layer structure formed from a mixture of a transport material and / or an electron transport material.
[0011]
In the example shown in FIG. 1, a translucent anode 4a is provided between the organic red light emitting medium 3c and the organic green light emitting medium 3b among the plurality of stacked organic light emitting media.. In FIG.From the electrode 4a, both of the adjacent organic light emitting media, that is, the organic green light emitting medium 3b and the organic red light emitting medium in FIG.3c elementIs configured. The translucent cathode 2a and the cathode 2c are commonly connected to a power source. Electrons are injected from the translucent cathode 2a into the organic blue light-emitting medium 3a and organic green light-emitting medium 3b, and from the cathode 2c into the organic red light-emitting medium 3c, and recombined with holes injected from the electrode 4a. The light emitting medium emits EL. The EL from each organic light emitting medium is synthesized and can be taken out through the substrate.
[0012]
In FIG. 1, if the work function of the cathode 2c is made smaller than that of the semitransparent cathode 2a, the electron injection efficiency of the organic red light emitting medium 3c can be increased as compared with the injection to other organic light emitting media. Even when a material system having low emission efficiency of red light emission is used, the control of the luminance balance between the green light emission medium 3b and the blue light emission medium 3a is easier than the conventional method. Also,Figure 1In this case, only two electrodes exist in the optical path for extracting light, and it is not necessary to provide an insulating film or substrate as in the conventional method (FIG. 5) in which a plurality of light emitting cells are stacked. There is an advantage that reduction can be reduced.
[0013]
In FIG.Two of the three organic light emitting media are formed between the same electrode pairs. In the present invention, as shown in FIG. 3, two electrodes for dividing the organic light emitting medium are provided, and the organic red light emitting medium 3c is provided. If the organic green light emitting medium 3b and the blue light emitting medium 3a are made independent, the control of the luminance balance of light emission becomes easier. still,Figure 1Semi-transparent cathode with one power source2aAnd cathode2cHowever, in FIG. 3, the semitransparent cathode 2b and the cathode 2c and the semitransparent anode 4b and the semitransparent anode 4a are connected in common. The brightness balance may be controlled.
[0014]
In the present invention, the organic thin film layer of the organic light emitting medium in the organic thin film EL device is formed by vacuum deposition, molecular beam deposition (MBE) or dipping of a solution dissolved in a solvent, spin coating, casting, bar coating, It can be formed by a known method using a coating method such as a roll coating method. The light emitting material of the organic light emitting medium is not particularly limited, and a known light emitting material can be applied. As a blue light emitting material constituting the organic blue light emitting medium, for example, a metal complex of 8-quinolinol and its derivatives described in US Pat. No. 5,167,671 and US Pat. No. 5,294,870, and a perylene or coumarin derivative are doped into the metal complex. Examples thereof include a distyrylarylene derivative and a distyrylarylene derivative doped with a fluorescent dye in JP-A-6-9953, which are excellent in performance and can be cited as representatives. Examples of the light-emitting material forming the organic green light-emitting medium include tris (8-quinolinolato) aluminum, quinacridone derivatives, xanthene dyes, coumarin derivatives, and the like, which are excellent in performance. Examples of the light-emitting material forming the organic red light-emitting medium include azine dyes, coumarin derivatives, xanthene dyes, merocyanine dyes, acridine dyes, and phthalocyanine dyes.
[0015]
It is also effective to provide a hole injection / transport layer in the organic light emitting medium of the organic thin film EL device of the present invention as necessary. Although it does not specifically limit as a positive hole transport material, For example, a triphenyldiamine derivative, an oxadiazole derivative, a porphyrin derivative, a stilbene derivative, an arylamine derivative etc. can be used. In the present invention, it is also effective to provide a blocking layer between the hole transport layer and the light emitting layer in order to increase the light emission efficiency. The blocking layer is responsible for confinement of excitons generated in the light emitting layer and confinement of electrons injected from the cathode into the light emitting layer. The compound to be used for the blocking layer is not particularly limited as long as it does not extremely impede the hole injection property, but it is desirable that the excitation energy is larger than that of the adjacent light emitting layer material. . Examples of compounds that can be used as a blocking layer in the present invention include known triphenyldiamine derivatives, oxadiazole derivatives, hydrazone derivatives, butadiene derivatives, styryl derivatives, pyrazoline derivatives, benzidine derivatives, and the like, as long as the light emission efficiency is not reduced. It is done. In the present invention, it is also effective to provide a hole injection layer between the hole transport layer and the anode. The hole injection layer is introduced in order to achieve stable hole injection from the anode, but it must have a role of maintaining the adhesion between the organic thin film layer and the anode (Applied Physics, Vol. 64, No. 64). No. 12, 1230-1233). The hole injection layer applicable in the present invention is, for example, spiro compounds, azo compounds, quinone compounds, indigo compounds, diphenylmethane compounds, quinacridone compounds, polymethine compounds, acridine compounds, porphyrins described in “Dye Handbook: Kodansha '86”. A condensed polycyclic dye such as a compound can be used. Further, low molecular organic P-type semiconductors described in “Organic Semiconductors: VERLAG CHEMIE'74” such as aromatic amines can also be applied.
[0016]
In the present invention, if necessary, an electron injection / transport zone may be provided between the light emitting layer and the cathode. The electron injecting / transporting material is not particularly limited, but 8-hydroxyquinolinol and derivatives thereof, oxadiazole derivatives, diphenylquinone derivatives, alkaline earth oxides such as SrO, CaO, BaO (Japanese Patent Laid-Open No. 6-163158). Application).
[0017]
The anode of the organic thin film EL element plays a role of injecting holes into the hole transport zone, and it is effective to have a work function of 4.0 eV or more. Specific examples of anode or translucent anode materials include indium tin oxide alloy (ITO), tin oxide (SnO2), Compounds containing gold, silver, platinum, copper and the like can be applied. The cathode is preferably a material having a low work function for the purpose of injecting electrons into the electron transport band or the light emitting layer, and is not particularly limited, but specifically, indium, aluminum, magnesium, magnesium-indium alloy, magnesium-aluminum alloy. Aluminum-lithium alloy, aluminum-scandium-lithium alloy, etc. can be used. Examples of the semitransparent cathode material include ITO and SnO described in JP-A-6-163158.2If an alkaline earth metal oxide such as SrO or CaO is provided at 0.1 to 1 nm at the interface between the semitransparent cathode material and the organic thin film layer, effective electron injection is achieved.
[0018]
For the purpose of protecting the element from oxygen and moisture, a long-life drive can be achieved even in the atmosphere by providing a sealing layer composed of inorganic compounds such as metal oxides, metal sulfides, metal fluorides, and known organic compounds. Can be guaranteed.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
【Example】
Hereinafter, examples of the present invention will be described in detail. Specific examples for obtaining white light emission are shown and compared with comparative examples.
[0020]
Example 1
A first embodiment of the present invention will be described with reference to FIG. The procedure for producing the organic thin film EL element used in Example 1 of the present invention will be described below. SnO which is a semi-transparent cathode on a glass substrate 1 which has been sufficiently cleaned2Then, 0.5 nm of SrO as an electron injection layer was formed. Subsequently, after forming 18 nm of tris (8-quinolinolato) aluminum (hereinafter abbreviated as Alq) of an electron transport layer by ultra high vacuum by MBE method, a distyryl biphenyl derivative (hereinafter abbreviated as DPVBi) represented by the following chemical formula 1 is formed. ) As a host material that emits blue light, and a guest material (hereinafter abbreviated as BczVBi) represented by Chemical Formula 2 is formed to a thickness of 35 nm under an ultrahigh vacuum so that 3.1 mol% of the host material is contained. The blue light emitting medium 3a is completed.
[0021]
[Chemical 1]
Figure 0004477150
[0022]
[Chemical 2]
Figure 0004477150
[0023]
Next, Alq is formed on the organic blue light emitting medium 3a at 35 nm under ultrahigh vacuum, and N, N′-biphenyl-N, N′-bis (α-naphthyl) -1, as a hole transport layer is further formed on Alq. 1′-biphenyl-4,4′-diamine (hereinafter abbreviated as α-NPD) is formed to a thickness of 30 nm under high vacuum, and the organic green light emitting medium 3b is formed in contact with the organic blue light emitting medium 3a.
[0024]
Next, after forming a semi-transparent anode 4a made of indium and zinc to 200 nm in a low temperature process, α-NPD which is a hole transport layer of the organic red light emitting medium 3c is formed to 40 nm under high vacuum, and further Alq is used as a host material As a guest material, 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (hereinafter abbreviated as DCM), which is a red fluorescent dye, is used. The organic red light-emitting medium 3c is formed by forming 50 nm under high vacuum so as to contain 1.8 mol%.
[0025]
Finally, an aluminum alloy containing 1 mol% of scandium as the cathode 2c is evaporated by RF sputtering in argon gas, and lithium is evaporated from a resistance heating source so that lithium accounts for 0.3 mol% of the cathode. It formed 20 nm. Further, an aluminum alloy containing 1 mol% of scandium as a cathode protective layer was formed to 300 nm by RF sputtering in argon gas.
[0026]
In this manner, the organic thin film EL element of Example 1 of the present invention having R, G, B organic light emitting media is completed. When the organic thin film EL element produced as described above has the semi-transparent cathode 2a and the cathode 2c in common, and the semi-transparent anode 4a is connected to a direct current power source and applied with a voltage to emit light, it is about 10V. 4520 cd / m2Was obtained. Compared with Comparative Example 1 using the conventional structure shown in FIG. 4, the luminance is improved by about 3.6 times. This is presumably because the use of the organic thin film EL device of the present invention improved the carrier injection / transport efficiency and the emission quantum efficiency over the conventional device shown in Comparative Example 1. 100 cd / m2The CIE chromaticity coordinates at X were 0.3 = 0.345 and Y = 0.361, and white light emission could be extracted.
[0027]
(Example 2)
Among organic light-emitting media, Alq which is an electron transport layer of the organic blue light-emitting medium 3a is formed to 18 nm, and a hole-transporting polyvinyl carbazole (hereinafter abbreviated as PVK) binder has a molar ratio of DPVBi and BczVBi. The organic thin film EL device was prepared in the same manner as in Example 1 except that the organic light emitting layer was formed to a thickness of 35 nm by a spin coating method. When the organic thin film EL element produced as described above has the semitransparent cathode 2a and the cathode 2c in common, and the semitransparent anode 4a alone is connected to a DC power source to apply a voltage to emit light, the voltage is about 2860 cd at 10V. / M2Was obtained. Compared with Comparative Example 2, the luminance is improved about 2.9 times. 100 cd / m2The CIE chromaticity coordinates at X were 0.328 and Y = 0.382, and almost white light emission could be extracted.
[0032]
(Example 3) With reference to FIG.Example 3Will be described. Example 3 differs from Example 1 to Reference Example 2 in that the organic light-emitting medium is divided into three by a semitransparent electrode. In the following, the present inventionExample 3The preparation procedure of the organic thin-film EL element used for will be described. After forming ITO which is a semitransparent anode 4b on a glass substrate 1 which has been sufficiently cleaned, 5 nm of CuPc is formed as a hole injection layer, and α-NPD which is a hole transport layer is further formed thereon at 40 nm under high vacuum. Formed. Next, DPVBi is used as a host material that emits blue light, and a guest material (BczVBi) is formed at 45 nm under an ultrahigh vacuum so that 3.1 mol% of the host material is contained in the host material. The organic blue light emitting medium 3a is completed by forming 20 nm under high vacuum. On the organic blue light emitting medium 3a, as a translucent cathode 2b for injecting electrons into the organic blue light emitting medium 3a, 0.5 nm of SrO is formed, and then a transparent electrode made of indium and zinc is further laminated. A semi-transparent cathode 2b capable of injecting electrons into both the organic blue light emitting medium 3a and the organic green light emitting medium 3b is completed by forming SrO at 0.5 nm on the upper part. Next, 50 nm of Alq as a light emitting layer and 50 nm of α-NPD as a hole transport layer are formed on the semi-transparent cathode 2b to complete the organic green light emitting medium 3b. A semitransparent anode 4a made of indium and zinc was formed on the organic green light emitting medium 3b. Subsequently, α-NPD of the hole transport layer was formed at 30 nm under high vacuum, Alq was used as a host material, DCM as a red fluorescent dye was used as a guest material, and DCM was 1.8 mol% with respect to Alq. The organic red light emitting medium 3c is formed by forming 50 nm under high vacuum so as to be included. Finally, an aluminum alloy containing 1 mol% scandium as the cathode 2c is evaporated by RF sputtering in argon gas, and lithium is evaporated from a resistance heating source so that lithium accounts for 0.3 mol% of the cathode. Formed. Further, an aluminum alloy containing 1 mol% of scandium as a cathode protective layer was formed to 300 nm by RF sputtering in argon gas.
[0033]
In this way, the present invention having R, G, B organic light-emitting media can be used.Example 3The organic thin film EL element is completed. When the organic thin-film EL element produced as described above is connected to a DC power source with the semitransparent cathode 2b and the cathode 2c in common and the semitransparent anodes 4a and 4b in common, a voltage is applied and light is emitted. About 4015 cd / m2Was obtained. Compared with Comparative Example 3 using the structure in which the conventional light emitting cells shown in FIG. 5 are stacked, the luminance is improved by about 4.7 times. 100 cd / m2The CIE chromaticity coordinates at X were 0.345 and Y = 0.371, and white light emission could be extracted.
[0034]
Although white light emission is obtained in this embodiment, light emission other than white light can be obtained by driving so that at least one of the R, G, and B light-emitting media divided by the semitransparent electrode is not made to emit light. Is also possible.
[0035]
(Example 4) Among organic light emitting media, organic blue light emitting medium 3a is dispersed in a PVK binder such that DPVBi and BczVBi are in a molar ratio of 100: 3, and an organic light emitting layer is formed to a thickness of 70 nm by spin coating. In addition to forming 20 nm of Alq as an electron transport layer,Example 3An organic thin film EL device was prepared in the same manner as described above. When the organic thin film EL element produced as described above is connected to a DC power source with the semitransparent cathode 2b and the cathode 2c in common and the semitransparent anodes 4a and 4b in common, a voltage is applied and light is emitted. About 3140 cd / m2Was obtained. Compared with Comparative Example 4 using the conventional structure shown in FIG. 5, the luminance is improved about 6 times. This is because the use of the organic thin film EL element of the present invention improved the light extraction efficiency over the conventional element shown in Comparative Example 4. 100 cd / m2The CIE chromaticity coordinates in X were 0.34 and Y = 0.369, and white light emission could be extracted.
[0036]
(Comparative Example 1)
The organic thin film EL element of Comparative Example 1 will be described below with reference to FIG. SnO which is a translucent anode 4a on a glass substrate 1 which has been sufficiently cleaned2In this order, α-NPD which is a hole transport layer is formed to 35 nm under ultra high vacuum, and then DPVBi is used as a blue light emitting host material as the organic blue light emitting medium 3a, and the guest material (BczVBi) is the host material. The film was formed in an ultrahigh vacuum of 35 nm so as to contain 3.1 mol% with respect to the material. Next, Alq is formed as an organic green light-emitting medium 3b on the organic blue light-emitting medium 3a under an ultrahigh vacuum at 35 nm. Further, Alq is used as a host material on Alq, DCM which is a red fluorescent dye is used as a guest material, and DCM is formed. The organic red light emitting medium 3c was formed by forming 30 nm under high vacuum so as to contain 1.8 mol% with respect to Alq. Finally, an aluminum alloy containing 1 mol% of scandium as the cathode 2c is evaporated by RF sputtering in argon gas, and lithium is evaporated from a resistance heating source so that lithium accounts for 0.3 mol% of the cathode. It formed 20 nm. Further, an aluminum alloy containing 1 mol% of scandium as a cathode protective layer was formed to 300 nm by RF sputtering in argon gas.
[0037]
In this manner, the organic thin film EL element of Comparative Example 1 of the present invention in which R, G, and B organic light emitting media are stacked is completed. When the organic thin film EL element produced as described above was made to emit light by applying a DC voltage, it was about 1270 cd / m at 10V.2Was obtained. 100 cd / m2The CIE chromaticity coordinates at X were 0.267 and Y = 0.458, and no white light emission was obtained.
[0038]
(Comparative Example 2)
The organic thin film EL element of Comparative Example 2 will be described below. SnO which is a translucent anode 4a on a glass substrate 1 which has been sufficiently cleaned2After forming CuPc, which is a hole injection layer, in order, the organic blue light emitting medium 3a is dispersed in a PVK binder so that DPVBi and BczVBi are in a molar ratio of 100: 3. An organic thin film EL element was prepared and evaluated in the same manner as in Comparative Example 1 except that the organic light emitting layer was formed to a thickness of 70 nm by the method. When a direct current voltage was applied to the organic thin film EL device prepared in Comparative Example 2 to emit light, it was about 970 cd / m at 10V.2Was obtained. 100 cd / m2The CIE chromaticity coordinates at X were 0.277 and Y = 0.450, and no white light emission was obtained.
[0039]
(Comparative Example 3)
In Comparative Example 3, as shown in FIG. 5, an organic thin film EL device for obtaining a synthetic light emission by stacking a plurality of organic light emitting cells was prepared. The method for producing the organic thin film EL element of Comparative Example 3 will be described below. After forming ITO, which is a translucent anode 4b, on a glass substrate 1 that has been sufficiently cleaned, copper phthalocyanine (hereinafter abbreviated as CuPc) is formed as a hole injection layer to a thickness of 5 nm, and further, α- NPD was formed to 40 nm under high vacuum. Next, DPVBi is used as a host material that emits blue light, and a guest material (BczVBi) is formed at 45 nm under an ultrahigh vacuum so that 3.1 mol% of the host material is contained in the host material. It was formed at 20 nm under high vacuum. On top of this, 0.5 nm of SrO is formed as a semi-transparent cathode 2b, and then a transparent electrode made of indium and zinc is laminated by a low temperature process to form a first organic light emitting cell that emits blue light. An insulating film 5 made of GeO was provided to a thickness of 25 nm on the first light emitting cell in order to separate the first light emitting cell and the second light emitting cell. Next, a second organic light emitting cell is formed on the GeO. After forming the semitransparent anode 4a made of indium and zinc on GeO, α-NPD as a hole transport layer is formed to 50 nm and Alq as a light emitting layer is formed to 50 nm. Next, after forming 0.5 nm of SrO as the semitransparent cathode 2b, a transparent electrode made of indium and zinc is laminated to form a second organic light emitting cell that emits green light. An insulating film 5 made of GeO was provided on the second light emitting cell to separate the second light emitting cell and the third light emitting cell by 25 nm. Next, a third organic light emitting cell is formed on the GeO. After forming a semitransparent anode 4a made of indium and zinc on GeO, α-NPD as a hole transport layer is formed to 50 nm, and Alq is added so that DCM is contained at 1.8 mol% with respect to Alq as a light emitting layer. Form 50 nm under high vacuum. Finally, an aluminum alloy containing 1 mol% scandium as the cathode 2c is evaporated by RF sputtering in argon gas, and lithium is evaporated from a resistance heating source so that lithium accounts for 0.3 mol% of the cathode. Formed. Further, an aluminum alloy containing 1 mol% of scandium as a cathode protective layer is formed to 300 nm by RF sputtering in argon gas, thereby completing the third organic light emitting cell.
[0040]
In this manner, an organic thin film EL element of Comparative Example 3 of the present invention in which organic light emitting cells are stacked is completed. When each organic light emitting cell of the organic thin-film EL element prepared as described above was connected to a DC power source and a voltage was applied, when 10 V was applied to each light emitting cell, about 850 cd / m.2Was obtained. 100 cd / m2The CIE chromaticity coordinates in X were X = 0.286, Y = 0.495, and no white light emission was obtained.
[0041]
(Comparative Example 4)
A method for producing the organic thin film EL element of Comparative Example 4 will be described. After forming ITO, which is a translucent anode 4b, on a glass substrate 1 that has been sufficiently cleaned, CuPc is formed to have a thickness of 25 nm as a hole injection layer, so that DPVBi and BczVBi have a molar ratio of 100: 3 in the PVK binder. Organic thin-film EL in which a plurality of organic light-emitting cells are stacked in the same manner as in Comparative Example 3 except that an organic light-emitting layer is formed by spin coating to form 70 nm and an electron transport layer of Alq is formed thereon by 20 nm. A device was created.
[0042]
When each organic light emitting cell of the organic thin film EL element produced as described above was connected to a DC power source and a voltage was applied, each voltage was about 525 cd / m when 10 V was applied to the light emitting cell.2Was obtained. 100 cd / m2The CIE chromaticity coordinates in X were 0.283 and Y = 0.461, and no white light emission was obtained.
[0043]
【The invention's effect】
In an organic thin-film EL device in which a plurality of organic light emitting media are laminated, an electrode is provided at the interface of the organic light emitting medium, and electric charges are injected from both the electrodes to both adjacent organic light emitting media. By controlling the intensity with voltage, it is easy to control the luminance balance, which is difficult in the organic thin film EL element in which conventional organic light emitting media are laminated, and low voltage and high luminance combined light emission can be obtained. In addition, the light extraction efficiency is improved and the manufacturing process can be simplified as compared with the conventional method of taking out synthetic light emission by stacking a plurality of light emitting cells.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an organic thin film EL element in which a plurality of light emitting media used in Example 1 and Example 2 of the present invention are stacked.
FIG. 3 of the present inventionExample 3as well asExample 4It is explanatory drawing of the organic thin-film EL element formed by laminating | stacking the several light emission medium used by.
4 is an explanatory diagram of a conventional organic thin film EL element in which a plurality of light emitting media used in Comparative Example 1 and Comparative Example 2 are stacked. FIG.
FIG. 5 is an explanatory diagram of a conventional organic thin film EL element that extracts light by stacking a plurality of organic EL cells used in Comparative Example 3;
[Explanation of symbols]
1 Substrate
2a translucent cathode
2b translucent cathode
2c cathode
3a Organic blue light emitting medium
3b Organic green luminescent medium
3c Organic red light emitting medium
4a translucent anode
4b translucent anode
5 Insulating film
6a Organic blue light emitting cell
6b Organic green light emitting cell
6c Organic red light emitting cell

Claims (3)

基板上に少なくとも一方が透明な複数の電極によって挟持された複数の積層された有機発光媒体を有する有機薄膜EL素子において、
前記複数の積層された有機発光媒体は、有機青色発光層を含む有機青色発光媒体、有機緑色発光層を含む有機緑色発光媒体、有機赤色発光層を含む有機赤色発光媒体を、前記基板側からこの順に積層してなり、
前記複数の積層された有機発光媒体の少なくとも前記有機赤色発光媒体前記有機緑色発光媒体の界面に隣接する二つの前記有機発光媒体の両方に同じ種類の電荷を注入できる電極を有し、
前記複数の電極と前記有機発光媒体の界面に設けられた電極が、負極と正極が交互となるように設定され、
前記複数の電極のうち前記有機赤色発光媒体に接する側の負極が、前記有機赤色発光媒体以外の前記有機発光媒体に接する側の負極よりも仕事関数が小さな材料よりなることを特徴とする有機薄膜EL素子。
In an organic thin film EL element having a plurality of stacked organic light emitting media sandwiched by a plurality of electrodes at least one of which is transparent on a substrate,
The plurality of stacked organic light emitting media includes an organic blue light emitting medium including an organic blue light emitting layer, an organic green light emitting medium including an organic green light emitting layer, and an organic red light emitting medium including an organic red light emitting layer from the substrate side. Laminated in order,
Wherein at least the interface of the organic red-light-emitting medium and the organic green light emitting medium of the plurality of stacked organic light emitting medium has an electrode capable of injecting two adjacent said organic both the same type of charge of the light-emitting medium,
Wherein the plurality of electrodes and the organic light emitting medium interface provided with electrodes is set as a negative electrode and the positive electrode is alternately
The organic thin film characterized in that the negative electrode on the side in contact with the organic red light emitting medium among the plurality of electrodes is made of a material having a work function smaller than that of the negative electrode on the side in contact with the organic light emitting medium other than the organic red light emitting medium. EL element.
有機発光媒体が少なくとも1つの有機発光層と、正孔注入・輸送帯及び/又は電子注入・輸送帯との積層構造であることを特徴とする請求項1記載の有機EL素子。  2. The organic EL device according to claim 1, wherein the organic light emitting medium has a laminated structure of at least one organic light emitting layer and a hole injection / transport zone and / or an electron injection / transport zone. 有機発光媒体のうち少なくとも1つが正孔輸送又は電子輸送性のバインダー中に発光材料を分散させた発光層を少なくとも1層有することを特徴とする請求項1記載の有機薄膜EL素子。  2. The organic thin film EL device according to claim 1, wherein at least one of the organic light emitting media has at least one light emitting layer in which a light emitting material is dispersed in a hole transporting or electron transporting binder.
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